The present invention relates to a roof structure, and more particularly to composite roof structures which take advantage of natural phenomena to maintain insulation layers at their highest thermal insulating efficiency.
The present invention relates to a composite roof structure and a method using the structure in such way that it takes advantage of natural phenomena to extract moisture from the insulation. Moisture manifests itself in different forms and can change from one physical state to another. In the liquid state, it is usually referred to as water. In the solid state, it is usually referred to as ice or snow. In the gaseous state, it is usually referred to as water vapor. By gravity, water will drain only in a downward direction; whereas, water vapor will migrate in any direction--up, down, or laterally--dependent upon relative vapor pressure. As a natural phenomenon, water vapor will always attempt to migrate from an area of higher vapor pressure to an area of lower vapor pressure. At such place and time that the water vapor reaches a condition known as its dewpoint it will condense taking the form of water. If such condensation of water vapor occurs within a permeable insulation layer of a roof structure, the insulation layer will become moisture laden thereby reducing their thermal insulating efficiency. If channels are provided within the lower insulation layer, the condensation water can drain away by gravity. If the temperature of standing water falls below 0.degree. C., it will turn to ice. Under certain conditions of very low humidity, ice can change to the vapor state by a phenomeon known as sublimation. If the temperature rises above 0.degree. C., the ice will turn to water. If the humidity conditions change in favor of doing so, the water can return to the vapor state and move about again as a vapor.
On earth, the weather patterns change as the earth tilts on its axis causing the seasons of the year, known as Spring, Summer, Autumn and Winter. Extremes in temperature and humidity occur during the seasons known as Summer and Winter. During winter, the temperature and humidity are usually lowest. In Summer, the temperature and humidity are usually highest.
The presence of moisture decreases the thermal efficiency of most types of insulation material. During Summer months under conditions of high humidity, water vapor tends to migrate from the atmosphere into the roof insulation of air conditioned buildings. There the water vapor condenses to water near the deck level, each time conditions for a dewpoint are reached. Over a period of time a substantial volume of water can build up resulting in the insulation becoming saturated with water thereby reducing the efficiency of the insulation. This water is difficult to remove and the reduced efficiency of the insulation leads to a substantial waste of energy.
Although the phenomena outlined above are well-known to meterologists, designers and constructers have not heretofore provided adequately for removal of moisture from roof insulation and for prohibition of seasonal ingress of moisture into the roof insulation. Although the prior art has provided for year-round venting, as exemplified by U.S. Pat. No. 2,192,458 to Swenson et al., the prior art has not provided for sealing out the vapor ingress which occurs during the Summer months as will be discussed, supra. Furthermore, the prior art has not provided for drainage channels and other adaptations or adjustments in configuration necessary to maximize the use of the natural phenomena to extract moisture from roofing insulation during Winter months. Because the roof structure of the present invention results in substantial energy savings there exists a need to teach designers and constructors the techniques of the present invention for minimizing the amount of moisture permitted to enter the roof insulation layers and for utilizing the forces of nature to maximize the extraction of moisture from the insulation layers.